In general, a base station system of a mobile communication network includes a base station main body part for processing transmission and reception signals, and an antenna part including a plurality of radiation elements to transmit and receive radio signals. The base station main body part is generally installed at a low location on the ground, the antenna part is installed at a high location, such as the top of a building or a tower, and the base station main body part is connected to the antenna part through a feeder cable.
Lately, as towers can be easily installed by virtue of miniaturization and weight reduction of devices for processing radio signals, a structure of installing a Remote Radio Head (RRH) in charge of processing of transmission and reception radio signals in front of an antenna is widely used in order to compensate for loss on coaxial cables typically used for transmission of signals between the base station main body part and the antenna part.
That is, the base station main body part for processing transmission and reception signals is divided into an RF signal processing part and a baseband signal processing part, wherein the baseband signal processing part is included in the base station main body part, and the RF signal processing part is included in the RRH. In this case, the base station main body part can be considered as a “baseband unit”. At this time, the base station main body part (baseband unit) and the RRH may be configured to transmit transmission and reception signals through an optical cable according to an optical communication method, in consideration of, for example, signal loss on a coaxial cable.
FIG. 1 is a block configuration diagram schematically showing an example of a typical base station system including an RRH. In FIG. 1, a state in which a plurality of base station systems 10 are connected to a base station controller (for example, Mobility Management Entity/Gateway (MME/GW) of a Long Term Evolution (LTE) system) is shown. The base station system 10 is configured with a Base Band Unit (BBU) 11, a base station antenna, and a RRH 12 installed at the base station antenna side. The baseband unit 11 is connected to the RRH 12 through an optical cable 13.
Meanwhile, in order to satisfy a service subscriber's demand of requiring massive data services, studies into methods such as LTE MIMO technology for transmitting massive data efficiently in a limited frequency band are actively conducted. Also, studies into a method of intensively providing a data service to a smaller number of people by implementing a base station in unit of a smaller cell rather than a typical method of implementing a base station in unit of a macro cell, and into a femto cell base station for implementing the method are actively conducted. In this respect, the structure in which the base station 10 is configured with the base band unit 11 and the RRH 12 installed at the base station antenna side, as shown in FIG. 1, is very suitable to implement such a femto cell base station.
However, the structure in which the base band unit 11 is connected to the RRH 12 through an optical cable requires relatively high installation costs although the structure is suitable in view of signal quality or transmission capacity. Particularly, in downtown areas, the initial or additional installation of optical cables involves many limitations due to neighboring buildings, roads, and a urban landscape.
In order to overcome the problem, a method of connecting the baseband unit 11 to the RRH 12 through wireless communication is considered. However, in order to transfer massive data according to a wireless communication method, wireless communication equipment having a broad bandwidth and high-performance is required.